A feed-in tariff pays you for electricity generated by your solar PV system.

Under a net feed-in tariff, a premium is paid for any solar energy that goes back into the grid from your house. So if you have surplus energy generated by your solar panels, you get paid for it; and if you use all of the energy you generate it will be offset against your normal electricity bill.

Under a gross feed-in tariff you get paid for every unit of electricity generated by your solar panels, because all of the production goes to the grid.